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Sonji plots –9 on a number line to represent the depth of her sailboat underwater and labels it B. She plots positive 20 on the same number line to represent the height of her sailboat above water and labels it A. Sonji asks if B, the elevation below sea level, acts as an opposite to A, the elevation above sea level. What is the best answer to her question?

Although they are on opposite sides of sea level, they are not opposites since –9 and 20 are unequal distances from 0.

Because they are on opposite sides of sea level, they are considered be opposites.

Because they are not on opposite sides of zero on the number line, they are not opposites.

Although they are on opposite sides of 0 on the number line, the reason they are considered opposites is because they are the same distance from sea level.